1. Field of the Invention
The present invention relates to a diagnosis apparatus for an anti-lock braking system, and more particularly to a diagnosis apparatus for diagnosing an operating condition of solenoid valves and drive circuits for use in an anti-lock braking system for an automotive vehicle.
2. Description of Related Art
Hitherto a variety of diagnosis apparatuses for solenoid drive circuits installed in an anti-lock brake system (ABS) have been researched. Such diagnosis apparatuses are arranged to diagnose an operating condition of a solenoid drive circuit for controlling a solenoid valve which is installed in a hydraulic system of the ABS. A diagnosis apparatus that could be installed in the ABS is shown in FIG. 7 where a diagnosis circuit is installed in an electronic control unit (ECU) 100 of the ABS. In FIG. 7, a part relating to one solenoid 300 is shown. By turning on and off a MOS transistor of a solenoid drive circuit 230, a solenoid electric-current flowed to the solenoid 300 is controlled. The relay 400 disposed upstream of the solenoid 300 is turned on and off according to the output of a relay drive circuit 240. By inputting a drain voltage of the solenoid drive circuit 230 through a noise filter 200 to an A/D port of the controller microcomputer 190, the voltage between a drain and a source of the MOS transistor is monitored to decide as to whether the breakage or short-circuit of the solenoid 300 is generated. When a solenoid monitoring circuit 210 is continuously set in a turned-on condition for more than a predetermined time period, it is decided that the solenoid 300 or the solenoid drive circuit 230 is abnormal and an abnormal signal indicative of the abnormality of the solenoid 300 or the solenoid drive circuit 230 is inputted to the control microcomputer 190. The control microcomputer 190 controls the relay drive circuit 240 through an AND circuit 220 on the basis of the decision signal and sets the solenoid 300 into an inoperative condition. The solenoid monitoring circuit 210 is arranged as shown in FIG. 8. Facilitating the explanation thereof, only a hydraulic pressure control of the front right and left wheels of the automotive vehicle will be discussed. In this Figure, FRIN denotes a hold solenoid valve of the front right wheel, FROUT denotes a decreasing solenoid valve of the front right wheel, FLIN denotes a hold solenoid valve of the front left wheel, and FLOUT denotes a decreasing solenoid valve of the front left wheel. The solenoid monitoring circuit 210 is constituted by a comparator 260 for monitoring a voltage of the MOS transistor of the solenoid drive circuit 230, a reference voltage generator 320 for generating a reference voltage, counters 270 for measuring each turning-on time of each solenoid 300, and an OR gate 280. The comparator 260 outputs at a H-level signal according to the turning-on of the solenoid 300 and starts a clock counting by each reset of the counters 270. When the counter value of one counter 270 reaches a predetermined time T1, a carry signal is outputted from the counter 270 and inputted to the OR gate 280. When one of the four solenoids 300 has kept on an on-condition for the predetermined time T1, an abnormality decision signal is outputted to an OUT terminal. Herein, the time T1 is set at a time period longer than a normal on-time in the normal ABS operation time, and if the solenoid 300 is set at an on-condition for more than the time period T1, an abnormality decision is outputted. A delay timer 340 shown in FIG. 7 does not promptly turn off the relay drive circuit 240 so that the control microcomputer 190 can have a sufficient time for reading the abnormal signal even if the abnormal signal is generated. Thus, in case that the operating condition of the solenoid 300 and its solenoid drive circuit 210 are diagnosed by simulatingly turning on the solenoid 300 and outputting an abnormal signal to the OUT terminal, the supply of the electric power to the solenoid 300 is stopped and the relay drive circuit 240 is turned off. Accordingly, the output voltage of the solenoid drive circuit 230 becomes set in an off condition. This generates troubles such that the control microcomputer 190 is turned off before the detection of the simulatingly outputted abnormal signal and that the relay 400 is frequently turned on-and-off during this diagnosis. Therefore, in order to avoid such troubles, the delay timer 340 is installed to the diagnosis apparatus.
However, this apparatus is still insufficient for a diagnosis of the operating condition of the solenoid and the solenoid drive circuit. That is, as shown in a time chart of FIG. 9, when the solenoid valve FRIN is turned on by a long pulse which is longer than a time period T1 as shown in FIG. 9(a), the counter value of the FRIN counter 270 is counted up as shown in FIG. 9(e). When the counter value becomes greater than the time period T1, a carry signal is outputted from the counter 270 and a pulse signal indicative of the abnormality is outputted to an OUT terminal as shown in FIG. 9(i). The control microcomputer 190 executes diagnosis by detecting the pulse signal indicative of the abnormality, when the counter value of the FRIN counter 270 becomes greater than the time period T1. That is, the control microcomputer 190 detects as to whether the abnormal signal is outputted to the OUT terminal by continuously turning on the solenoid 300 for more than the predetermined time T1. If normal, the solenoid valve FRIN is set at H-level and then a H-level signal is outputted to the OUT terminal after a predetermined time elapsed. If abnormal, a L-level signal is outputted to the OUT terminal. The diagnosis as to the operating conditions of the solenoid 300 and the drive circuit 230 is executed by this signal output to the OUT terminal. Although the above mentioned diagnosis is executed for one solenoid 230, if it is executed by shifting it at predetermined intervals as shown in FIG. 9(b), FIG. 9(c) and FIG. 9(d), the respective counters 270 count as shown in FIG. 9(e), FIG. 9(f), FIG. 9(g) and FIG. 9(h). Therefore, the OUT terminal outputs four abnormal signals corresponding to diagnosis pulses as shown in FIG. 9(i). The control microcomputer 19 diagnoses as to whether all solenoids 300 and the solenoid drive circuits 230 thereof are operated normally, by reading the four signals.
However, this method has a problem that the diagnosis takes relatively long time since the time TI for counting up the counter is normally set at several seconds. The hydraulic pressure of a wheel cylinder of the brake hydraulic system is deviated in the order of pressure increase, hold, increase, non-set and increase as shown in FIG. 9. That is, it was necessary to operate a non-set mode which is not normally used and where only pressure decreasing solenoid valves shown by FROUT and FLOUT are turned on. Further, in order to solve the later mentioned problem, a solenoid monitor circuit 210 of a diagnosis apparatus has been proposed as shown in FIG. 10. The solenoid monitor circuit 210 further includes an AND gate 290 which is set at H by the carry signals of the counters 270 and a select circuit 330 which selects one of the output of the OR gate 280 and the output of the AND gate 290 by checking the selection signal from the control microcomputer 190, in addition to the solenoid monitoring circuit of FIG. 8. The solenoid monitoring circuit 210 enables the execution of the diagnosis without taking the non-set mode. The diagnosis circuit using the monitoring circuit 210 has a structure as the same as that shown in FIG. 7. The operation of solenoid monitoring circuit 210 is shown by a time chart of FIG. 11. During diagnosis, the control microcomputer 190 sets the select circuit 330 so as to select an output side of the AND gate 290 by setting a CHECK signal at a H-level as shown in FIG. 11(n). Next, the solenoids are, in turn, turned on as shown in FIG. 11 (a) to FIG. 11(d). With these turning on, the counters 270 are, in turned, counted up as shown in FIG. 11(e) to FIG. 11(h). Carry signals are outputted from the counters 270 which took a value greater than the predetermined time T1. When four carry signals are inputted to the AND gate 290 and when all counters 270 finished the counting of the predetermined time, a H-level signal is outputted to the OUT terminal. The OUT terminal is monitored by the control microcomputer 190. If at least one of the counters 270 is not operated, the AND gate 290 does not take H-level. Therefore, it becomes possible to diagnose all counters 270 by this operation. Since the wheel cylinder hydraulic pressure is deviated in the order of pressure increase, hold, decrease, and increase by flowing electric power to the solenoid, the hydraulic system is not set at the non-set mode during the diagnosis.
However, since in the pressure decrease condition the solenoid valves of the front two wheels are turned on as shown in FIG. 11(b) and FIG. 11(d), such proposed diagnosis apparatus causes a problem such that it cannot be adapted to a requirement of the control side that only one wheel is admitted to be set at a pressure decrease mode during the diagnosis, that is, during the ABS inoperative condition.